Financial Instruments, Risk Management and Fair Value measurements - Summary of Assets and Liabilities Fair Value Measured on a Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Liabilities:
Stock award expense	$ 0.3	$ 1.6
Fair Value, Measurements, Recurring
Assets:
Equity investments	1.8
Total assets	1.8
Liabilities:
Deferred compensation arrangement	2.0	0.7
Separation Related Reimbursement Awards	0.9	2.1
Total liabilities	2.9	2.8
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Equity investments	1.8
Total assets	1.8
Liabilities:
Deferred compensation arrangement	2.0	0.7
Separation Related Reimbursement Awards	0.9	2.1
Total liabilities	2.9	2.8
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 [Member]
Assets:
Equity investments	0.0
Total assets	0.0
Liabilities:
Deferred compensation arrangement	0.0	0.0
Separation Related Reimbursement Awards	0.0	0.0
Total liabilities	0.0	0.0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 [Member]
Assets:
Equity investments	0.0
Total assets	0.0
Liabilities:
Deferred compensation arrangement	0.0	0.0
Separation Related Reimbursement Awards	0.0	0.0
Total liabilities	$ 0.0	$ 0.0